1. Field of the Invention
The present invention relates to a semiconductor having a superlattice semiconductor layer and a method of manufacturing the same, and more particularly, to a semiconductor device having a GaN superlattice semiconductor layer for reducing a driving voltage by decreasing a series resistance and a method of manufacturing the same.
2. Description of the Related Art
A laser diode (LD) has a superlattice structure in which different materials are stacked to form a multi-layer. For example, a GaN based LD has a superlattice structure in which AlGaN and GaN are stacked in a sandwich structure as shown in FIG. 1. Such a GaN based LD requires AlGaN having a large amount of Al in order to improve an optical confinement. However, AlGaN having a large amount of Al increases a series resistance of the LD that causes an increase in a driving voltage of the LD. In addition, the increase in the driving voltage of the LD reduces the lifespan of the LD.
A GaN based material is studied to be applied to an optical device field, such as a light emitting diode (LED) and an LD. Decreases in an oscillation current and a driving voltage reduce an input power to an LD, resulting in the improvement of durability. Since Mg as a p-type dopant has a low doping efficiency, an increase in the driving voltage usually occurs in a p-type layer. Referring to the Japanese Laid-open Patent No. 13-308458 and the Japanese Laid-open Patent No. 14-111131, p-type layers in a GaN based LD include a p-GaN optical waveguide layer, a p-AlGaN/GaN optical confinement layer, and a p-GaN contact layer.
An optical confinement layer has a superlattice structure having a GaN layer interposed between AlGaN layers. The GaN layer interposed between the AlGaN layers in the optical confinement layer prevents cracks of the AlGaN layers having a large amount of Al. In addition, the superlattice structure having GaN and AlGaN increases a doping efficiency of a deep acceptor by forming two dimensional hole gas and increases a hole concentration by increasing the doping efficiency as well as generating a higher doping efficiency than a bulk AlGaN layer.
Studies for optimizing the p-type layers to prevent increases in the driving voltage of the GaN based LD take place by varying experimental conditions, for example, changing the thickness of a superlattice and the flows of dopants. However, such a method met the limitation to optimize the superlattice because AlGaN including a large amount of Al should be used for the optical confinement.
Accordingly, the series resistance should be reduced to increase the lifespan of the LD, so the amount of Al should be reduced to reduce the resistance of the superlattice structure. However, since the reduction of the amount of Al deteriorates the optical confinement, there is a limit of reducing the amount of Al.